|Baldwin, Ransom - Randy|
Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: 3/26/2004
Publication Date: 4/29/2004
Citation: Oba, M., Baldwin, R.L., Owens, S.L., Bequette, B.J. 2004. Utilization of ammonia-n by ruminal epithelial and duodenal mucosal cells isolated from growing sheep [abstract]. BARC Poster Day.
Technical Abstract: To determine the capability of ruminant gut tissues to detoxify ammonia-N, ruminal epithelial cells (REC) and duodenal mucosal cells (DMC) were isolated from growing Texel-Polypay ram lambs (n=4) fed a mixed forage-concentrate diet. Immediately after isolation, primary cells were incubated for 60 min with glucose (1mM), glutamate (1mM), [15N]ammonium chloride (0, 5, 10, 20, or 40 mM), and one of four combinations of substrate to support urea synthesis (1 mM each; control (no additional substrates), N-carbamoylglutamate (NCG), NCG + ornithine, NCG + ornithine + aspartate) in a 5 x 4 factorial arrangement of treatments. Incorporation of ammonia-15N into Ala, citrulline, Arg, and urea (nmol / 10 6 cells / 60 min) was determined by gas chromatography-mass spectrometry. Utilization of ammonia-N for net Ala synthesis increased quadratically from 0.73 to 1.35 nmol for DMC (P < 0.001) and from 0.28 to 0.69 nmol for REC (P < 0.001) as the ammonia concentration increased from 5 to 40 mM, regardless of substrate treatments. For both cell types, ammonia-N incorporation into Ala was lower in the presence of NCG compared to control (1.18 vs. 1.39 nmol for DMC, P < 0.001; 0.52 vs. 0.59 nmol for REC, P < 0.05). For REC, ammonia-N was not incorporated into citrulline, Arg and urea, whereas for DMC ammonia-N was incorporated into citrulline but not Arg and urea. However, ammonia-N utilization for net citrulline synthesis by DMC decreased linearly from 0.68 to 0.27 nmol (P < 0.001) as ammonia concentrations increased from 5 to 40 mM. Thus, in ruminant gut tissues, Ala synthesis is probably a more significant disposal pathway to detoxify ammonia-N at high ammonia concentrations compared with disposal via the ornithine-urea cycle although DMC also possess a capability to incorporate ammonia-N into citrulline.